[Scummvm-devel] Fastening text display in Scumm engine

[Nicolas Bonifas]

Hello,

I wrote a small patch that dramatically fastens text display in Scumm, 
by simply recording the values returned by unpackChar instead of 
computing them each time we need them.

It is only a proof of concept (I lack time to polish it at the moment):
- it needs better integration (I am new to Scummvm development)
- _unpackedChars array is probably useless: we should directly record 
the unpacked characters in _chars[].src and use this value whatever the 
value of _bpp
- every call to unpackChar needs to be replaced (for example, call from 
drawFrame)
- there may be a memory leak (I never free the _unpackedChars array).

Nevertheless, the results are very good. Here are the execution times 
for the ending sequence of COMI with and without the patch, in the same 
conditions (on a 1.5 Ghz processor). Included is the beginning of gprof 
flat profile.

with patch : 31.88 seconds
% time   seconds  calls   name
  46.80    14.92    58257  Normal2x(unsigned char const*, unsigned int, 
unsigned char*, unsigned int, int, int)
  15.18     4.84  1354665 
Scumm::NutRenderer::drawChar(Graphics::Surface const&, unsigned char, 
int, int, unsigned char)
  11.39     3.63   175576  Scumm::blit(unsigned char*, int, unsigned 
char const*, int, int, int)
   5.66     1.80    58081  OSystem_SDL::copyRectToScreen(unsigned char 
const*, int, int, int, int, int)

without patch : 51.81 seconds
% time   seconds  calls   name
  37.62    19.49  1354972  Scumm::NutRenderer::unpackChar(unsigned char)
  29.99    15.54    58188  Normal2x(unsigned char const*, unsigned int, 
unsigned char*, unsigned int, int, int)
   9.25     4.79  1354460 
Scumm::NutRenderer::drawChar(Graphics::Surface const&, unsigned char, 
int, int, unsigned char)
   6.62     3.43   175579  Scumm::blit(unsigned char*, int, unsigned 
char const*, int, int, int)
   3.38     1.75    58075  OSystem_SDL::copyRectToScreen(unsigned char 
const*, int, int, int, int, int)

Regards,
Nicolas
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